1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to an LCD device according to a liquid crystal dispensing method, and a method for manufacturing the same.
2. Discussion of the Related Art
Generally, ultra thin sized flat panel displays having a display screen with a thickness of several centimeters or less, and in particular, flat panel LCD devices, are widely used in monitors for notebook computers, spacecraft, and aircraft because such LCD devices have low power consumption because of a low driving voltage and are easy to carry.
Such LCD devices include a lower substrate, an upper substrate and a liquid crystal layer. A thin film transistor (TFT) and a pixel electrode are formed on the lower substrate. A light-shielding layer, a color filter layer and a common electrode are formed on the upper substrate, which is opposite to the lower substrate. Then, the liquid crystal layer is formed between the lower and upper substrates. In operation, an electric field is generated between the lower and upper substrates by the pixel and common electrodes, so that the alignment of molecules in the liquid crystal layer is driven by the electric field. Transmissivity of light through the liquid crystal layer is controlled with driving the liquid crystal layer, thereby displaying an image.
In manufacturing this LCD device, a vacuum injection method based on capillary phenomenon and pressure difference has been conventionally used to form the liquid crystal layer between lower and upper substrates. However, such a vacuum injection method has a problem in that it takes a long time to inject the liquid crystal due to the large sized display area, thereby reducing the productivity.
A liquid crystal dispensing method has been proposed to solve such a problem. A prior art method for manufacturing an LCD device based on the liquid crystal dispensing method will be explained with reference to FIG. 1A to FIG. 1D.
As illustrated in FIG. 1A, a lower substrate 1 and an upper substrate 3 are prepared. Although not shown in drawings, a plurality of gate and data lines are formed on the lower substrate 1. The gate lines cross the data lines to define pixel regions. A thin film transistor (TFT) is formed at each crossing point between the gate and data lines. A pixel electrode connected with the thin film transistor is formed in the pixel region.
A light-shielding layer is formed on the upper substrate 3 to prevent light from leaking out from the gate and data lines and the thin film transistor. Color filter layers of red(R), green(G), and blue(B) are formed on the light-shielding layer, and a common electrode is formed on the color filter layers. An alignment layer is formed on at least one of the lower substrate 1 and the upper substrate 3 to initially align molecules in a liquid crystal to be interposed between the upper and lower substrates 1 and 3.
As shown in FIG. 1B, main and dummy sealants 7, 8 are formed on the lower substrate 1. A liquid crystal 5 is dropped onto so that a liquid crystal layer is formed. A spacer (not shown) is spread onto the upper substrate 3 to maintain a cell gap. The main sealant 7 prevents the liquid crystal from flowing out, and bonds the lower and upper substrates to each other. The dummy sealant 8 is formed in the circumference of the main sealant 7 to protect the main sealant 7.
In the liquid crystal dispensing method, the liquid crystal layer is formed on the substrates before they are attached in a sealant hardening process. If a heat-hardening type sealant is used for the sealant, the liquid crystal which flows during the heating may be contaminated by the sealant. For this reason, a UV-hardening type sealant is used for the sealant in the liquid crystal dispensing method.
As shown in FIG. 1C, the lower substrate 1 is attached to the upper substrate 3.
Referring to FIG. 1D, the main sealant 7 is hardened by irradiating UV light onto the sealant with a UV irradiating device 9, thereby bonding the lower substrate 1 to the upper substrate 3.
As shown in FIG. 1E, the lower and upper substrates 1, 3 are cut into unit cells, thereby forming liquid crystal cells.
FIG. 2 illustrates a perspective view for showing cutting steps of the substrate into the unit cells.
As shown in FIG. 2, the bonded substrates are cut into unit cells. In the cutting step, after forming a cutting line (scribing process) on a surface of the bonded substrates by a scriber, such as a diamond pen with a hardness higher than glass of the substrates, a mechanical impact is applied to the bonded substrates along the cutting line by using a breaker (a breaking process), to obtain a plurality of unit cells at the same time. Alternatively, a pen or wheel of diamond may be used to carry out the scribing and the breaking in one step, to obtain the unit cell one by one.
Even though the cutting line 10 is not shown in FIG. 2, the plurality of cutting lines are formed to remove dummy regions of the circumference when practically cutting the cells.
FIG. 3 illustrates a plan view for showing the cell cutting line 10 of the lower substrate 1 on which the sealant 7,8 is formed. Referring to FIG. 3, the cutting line 10 is overlapped with a predetermined region (circle region) of the dummy sealant 8. At this time, the dummy sealant 8 is hardened in the UV irradiating step before cutting the substrate into the cells.
If the substrate is cut into the cells in the break process after the scribing process, a problem is not generated by the hardened dummy sealant 8. However, if the unit cell is obtained one by one by carrying out the scribing/breaking process at the same time, it is hard to cut the substrate into the cells due to the hardened dummy sealant 8.